The present invention relates to the field of digital image processing.
The sophistication and increased definition of displayed images, especially for high definition TV, has led to the development of various systems to, during transmission of moving images, transmit only a portion of these images, namely only the portion of the images which changes from one image to another.
FIG. 1 shows as exemplary general arrangement of a conventional TV image encoder. The encoder comprises a video signal input 1, an analog-digital converter (ADC) 2, a scanning system 3 for scanning images in blocks, a device for calculating the discrete cosine transform (DCT) 4, a quantification system (Q) 5, a varying length coding system (VLC) 6, and a buffer memory 7, the output of which is provided through a line 8 to the transmission channel or to an intermediate storing device (not shown). With the use of the cosine transform, the amount of information to be transmitted is reduced. In addition, a unit for comparing the current image with the previous image is provided. This system comprises devices for calculating reverse quantification (Q.sup.-1) 9 and reverse cosine transform (DCT.sup.-1) 10, the results of which are provided to a frame memory 11. Frame memory 11 contains, at a given time, the image preceding the current image. The content of this frame memory is compared by blocks to the content of the current image in a motion estimator 12. Motion estimator 12 seeks, for each current image block, the portion of the preceding image most resembling the current image block. This most resembling portion is called the target portion and the distance between the current image block of interest and this target portion is called motion vector D. This vector constitutes a first input of a predictor 14 which also receives the preceding frame from frame memory 11. The predictor output is sent back by an adder 15 into frame memory 11. A subtracter 16 subtracts, from current image information, the information of the preceding image output from the frame memory and shifted by the predictor, block after block. The output of subtracter 16 is provided to the DCT calculating device 4. Thus, at output 8 of the encoding system, one obtains a reduced amount of information, because the information has been subjected to two processings; the process for comparison with the preceding image and the cosine transform and quantification process. Hence, the bandwidth of the transmission channels is substantially decreased because less information needs to be transmitted.
FIG. 2 shows a decoder associated with the encoder of FIG. 1. The decoder receives at its input 20 a signal corresponding to the transmitted signal 8. This signal is processed by a variable length decoder (VLD) 21, a system for calculating the reverse quantification 22, and a system for calculating the reverse cosine transform 23. The output of the system for calculating the reverse cosine transform is provided to a block to line scanning converter 25, then to a digital/analog converter (DAC) 26 to provide a video signal 27 suitable, for example, to control a TV display system (not shown). In addition, the VLD system provides the motion vector D to a predictor 30, which also receives the output of a frame memory 31. The predictor output signal is added to the output of the circuit calculating the reverse cosine transform by an adder 32. The output of adder 32 is provided, on the one hand, to the frame memory 31 and, on the other hand, to the scanning converter 25.
The above description is intended only to exemplify an environment in which the invention can be applied. The invention specifically relates to the predictor 14 or 30 of the encoder or decoder; these predictors are of course identical, but for the sake of simplicity, the invention will be disclosed only in connection with the decoding circuit.
Up to now, the known predictors have been complex systems occupying a whole printed circuit board on which are arranged numerous components and especially numerous memories between which numerous interconnections are provided.